Mesoporous and macroporous nickel-based catalyst having a median macropore diameter of between 50 nm and 200 nm and its use with regard to hydrogenation

ABSTRACT

Disclosed are a supported catalyst, its method of preparation and use in hydrogenation methods, which catalyst contains an oxide substrate that is for the most part calcined aluminum and an active phase that contains nickel, with the nickel content between 5 and 65% by weight in relation to the total mass of the catalyst, with the active phase not containing a metal from group VIB, the nickel particles having a diameter that is less than or equal to 20 nm, the catalyst having a median mesopore diameter of between 14 nm and 30 nm, a median macropore diameter of between 50 and 200 nm, a mesopore volume that is measured by mercury porosimetry that is greater than or equal to 0.40 mL/g, and a total pore volume that is measured by mercury porosimetry that is greater than or equal to 0.42 mL/g.

FIELD OF THE INVENTION

The invention has as its object a catalyst that is supported on an oxide substrate that is for the most part calcined aluminum with an active nickel phase having a texture and a formulation that are favorable to hydrogenation reactions, in particular to reactions for selective hydrogenation of polyunsaturated compounds or for hydrogenation of aromatic compounds. The invention also relates to the method for preparation of said catalyst as well as its use in hydrogenation reactions.

The catalysts for selective hydrogenation or for hydrogenation of aromatic compounds are generally based on metals from group VIII of the periodic table such as nickel. The metal comes in the form of nanometric metal particles that are deposited on a substrate that may be a refractory oxide. The metal content of the group VIII, the optional presence of a second metal element, the size of the metal particles, and the distribution of the active phase in the substrate as well as the nature and pore distribution of the substrate are parameters that have an importance relative to the performance values of catalysts.

The speed of the hydrogenation reaction is governed by multiple criteria, such as the diffusion of reagents on the surface of the catalyst (external diffusional limitations), the diffusion of reagents in the porosity of the substrate to the active sites (internal diffusional limitations), and the inherent properties of the active phase such as the size of metal particles and the distribution of the active phase within the substrate.

As regards the size of the metal particles, it is generally assumed that the catalyst is all the more active the smaller the size of the metal particles. In addition, it is important to obtain a size distribution of the particles centered on the optimal value as well as a narrow distribution around this value.

As regards internal diffusional limitations, it is important that the pore distribution of the macropores and mesopores be adapted to the desired reaction so as to ensure the diffusion of reagents in the porosity of the substrate to the active sites as well as the diffusion to the outside of the products that are formed. The importance of an adapted pore distribution and in particular the presence of macropores in a reaction for selective hydrogenation of a pyrolysis gasoline in the case of a palladium-based catalyst has been described by, for example, Z. Zhou, T. Zeng, Z. Cheng, W. Yuan, in AICHE Journal, 2011, Vol. 57, No. 8, pages 2198-2206.

Numerous developments thus relate to the optimization of the pore distribution of the catalyst by the optimization of the substrate of the catalyst.

The document WO2011/080515 describes a nickel-based hydrogenation catalyst on an alumina substrate that has a nickel content of more than 35% by weight, with said catalyst having a high dispersion of nickel (0) on the surface of an alumina with very open porosity and with a high specific surface area. The pore distribution of the substrate is bimodal: at least 30% of the total pore volume consists of pores that have a diameter of between 5 and 20 nm, and at least 20% of the total pore volume consists of pores that have a diameter of between 100 and 700 nm with a total pore volume of the substrate of at least 1.0 mL/g. The nickel surface area should be greater than or equal to 110 m² per gram of nickel.

In this context, one of the objectives of this invention is to propose a supported catalyst with an active nickel phase that has hydrogenation performance values in terms of activity that are at least as good as the known catalysts of the state of the art.

More particularly, the invention relates to a supported catalyst that comprises an oxide substrate that is for the most part calcined aluminum and an active phase that comprises nickel, with the nickel content being between 5 and 65% by weight of said element in relation to the total mass of the catalyst, with said active phase not comprising a metal from group VIB, the nickel particles having a diameter that is less than or equal to 20 nm, said catalyst having a median mesopore diameter of between 14 nm and 30 nm, a median macropore diameter of between 50 and 200 nm, a mesopore volume that is measured by mercury porosimetry that is greater than or equal to 0.40 mL/g, and a total pore volume that is measured by mercury porosimetry that is greater than or equal to 0.42 mL/g.

The applicant discovered that a catalyst that is prepared by impregnation of the active phase on an alumina that results from the calcination of a particular alumina gel that is prepared according to the preparation method described below makes it possible to obtain a catalyst that has a pore distribution as well as a nickel particle size that are particularly suited to hydrogenation reactions, in particular to reactions for selective hydrogenation of polyunsaturated molecules such as diolefins, acetylenic compounds or alkenylaromatic compounds, or to reactions for hydrogenation of aromatic compounds.

Actually, the pore distribution resulting from the method for preparation of the calcined aluminum oxide substrate obtained from a specific alumina gel makes it possible to provide a porosity that is particularly suited to promoting the diffusion of reagents in the porous medium and then their reaction with the active phase. Without being linked to any theory, it seems that the particular textural properties of the catalyst according to the invention, in particular a bimodal porosity with the presence of macropores and mesopores of controlled size, make it possible to obtain a catalyst that has hydrogenation performance values in terms of activity that are at least as good as the known catalysts of the state of the art. The catalyst according to the invention is distinguished by a high mesopore volume with a high median mesopore diameter that is coupled with a consequent macropore volume but where said volume is not too high, with a median macropore diameter that is relatively small. Actually, it is well known that although the presence of a macropore volume can reduce the internal diffusional limitations, at the same time it weakens the mechanical strength of the catalyst. It is therefore important to control the percentage of the macropore volume in relation to the total pore volume as well as the median macropore diameter so as to obtain a catalyst that has the desired catalytic performance values and sufficient mechanical strength. In addition, the presence of a high total pore volume of the catalyst according to the invention makes it possible to impregnate a high content of active phase in a single pass.

According to a variant, the substrate, before introduction of the active phase, has a pore volume that is contained in the pores with a diameter of between 100 and 700 nm that is less than 20% of the total pore volume of the substrate, preferably less than 15% of the total pore volume of the substrate.

According to a variant, the nickel content is between 10 and 34% by weight of said element in relation to the total mass of the catalyst.

According to a variant, the macropore volume of the catalyst is between 5 and 40% of the total pore volume.

According to a variant, the mesopore volume of the catalyst is between 0.45 mL/g and 0.8 mL/g.

According to a variant, the catalyst does not contain micropores.

The invention also relates to the method for preparation of said catalyst. The invention also relates to the use of the catalyst in a hydrogenation method in which the catalyst according to the invention, or that which can be prepared according to the preparation method according to the invention, is brought into contact in the presence of hydrogen with a hydrocarbon feedstock that contains polyunsaturated molecules and/or aromatic compounds in such a way as to obtain an effluent that is at least partially hydrogenated.

DETAILED DESCRIPTION The Catalyst According to the Invention

The catalyst according to the invention comes in the form of a supported catalyst that comprises an oxide substrate that for the most part is calcined aluminum and a nickel-comprising active phase. The characteristics of the alumina gel that have led to obtaining the alumina that for the most part is contained in said substrate, as well as the textural properties obtained with the active phase, impart its specific properties to the catalyst according to the invention.

More particularly, the invention relates to a supported catalyst that comprises an oxide substrate that is for the most part calcined aluminum and a nickel-comprising active phase, with the nickel content being between 5 and 65% by weight of said element in relation to the total mass of the catalyst, with said active phase not comprising a metal from group VIB, the nickel particles having a diameter that is less than or equal to 20 nm, said catalyst having a median mesopore diameter of between 14 nm and 30 nm, a median macropore diameter of between 50 and 200 nm, a mesopore volume measured by mercury porosimetry that is greater than or equal to 0.40 mL/g, and a total pore volume that is measured by mercury porosimetry that is greater than or equal to 0.42 mL/g.

The catalyst according to the invention and the substrate that is used for the preparation of the catalyst according to the invention have particular textural properties, in particular a specific pore distribution, where the macropore and mesopore volumes are measured by mercury intrusion, and the micropore volume is measured by nitrogen adsorption.

“Macropores” are defined as pores whose openings are greater than 50 nm.

“Mesopores” are defined as pores whose openings are between 2 nm and 50 nm, inclusive.

“Micropores” are defined as pores whose openings are less than 2 nm.

Total pore volume of the catalyst or of the substrate used for the preparation of the catalyst according to the invention is defined as the volume that is measured by mercury intrusion porosimetry according to the Standard ASTM D4284-83 at a maximum pressure of 4000 bar (400 MPa), using a surface tension of 484 dyne/cm and a contact angle of 140°. The wetting angle was assumed to be equal to 140° by following the recommendations of the work “Techniques de l'ingénieur, traité analyse et caractérisation [Engineering Techniques, Analytical Treatise and Characterization],” pages 1050-1055, written by Jean Charpin and Bernard Rasneur.

So as to obtain better precision, the value of the total pore volume corresponds to the value of the total pore volume that is measured by mercury intrusion porosimetry that is measured on the sample minus the value of the total pore volume measured by mercury intrusion porosimetry measured on the same sample for a pressure that corresponds to 30 psi (approximately 0.2 MPa).

The volume of the macropores and mesopores is measured by mercury intrusion porosimetry according to the Standard ASTM D4284-83 at a maximum pressure of 4000 bar (400 MPa), using a surface tension of 484 dyne/cm and a contact angle of 140°. The value beyond which the mercury fills all of the intergranular gaps is set at 0.2 MPa, and it is considered that beyond this, the mercury penetrates into the pores of the sample.

The macropore volume of the catalyst or of the substrate that is used for the preparation of the catalyst according to the invention is defined as being the cumulative volume of mercury introduced at a pressure of between 0.2 MPa and 30 MPa, corresponding to the volume that is contained in the pores with an apparent diameter of greater than 50 nm.

The mesopore volume of the catalyst or of the substrate that is used for the preparation of the catalyst according to the invention is defined as being the cumulative volume of mercury that is introduced at a pressure of between 30 MPa and 400 MPa, corresponding to the volume that is contained in the pores with an apparent diameter of between 2 and 50 nm.

The volume of the micropores is measured by nitrogen porosimetry. The quantitative analysis of the microporosity is carried out starting from the method “t” (Lippens-De Boer Method, 1965), which corresponds to a transform of the initial adsorption isotherm as described in the work “Adsorption by Powders and Porous Solids. Principles, Methodology and Applications” written by F. Rouquérol, J. Rouquérol, and K. Sing, Academic Press, 1999.

The median mesopore diameter is also defined as being the diameter such that all of the pores, among all of the pores that constitute the mesopore volume, of a size less than this diameter constitute 50% of the total mesopore volume determined by mercury intrusion porosimetry.

The median macropore diameter is also defined as being the diameter such that all of the pores, among all of the pores that constitute the macropore volume, of a size that is less than this diameter constitute 50% of the total macropore volume that is determined by mercury intrusion porosimetry.

The specific surface area of the catalyst or of the substrate used for the preparation of the catalyst according to the invention is defined as the B.E.T. specific surface area that is determined by nitrogen adsorption in accordance with the Standard ASTM D 3663-78 established starting from the BRUNAUER-EMMETT-TELLER method that is described in the periodical “The Journal of American Society,” 60, 309, (1938).

Below, the groups of chemical elements are provided according to the CAS classification (CRC Handbook of Chemistry and Physics, CRC Press Editor, Chief Editor D. R. Lide, 81^(st) Edition, 2000-2001). For example, group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IUPAC classification.

Characteristics of the Substrate According to the Invention

The majority of the substrate of the catalyst according to the invention comprises a calcined aluminum porous oxide.

Said substrate has a calcined alumina content that is greater than or equal to 90% by weight in relation to the total weight of said matrix, optionally completed by silica and/or phosphorus with a total content of at most 10% by weight of an equivalent of SiO₂ and/or P₂O₅, preferably less than 5% by weight, and in a very preferred manner less than 2% by weight in relation to the total weight of said matrix. The silica and/or the phosphorus can be introduced by any technique that is known to one skilled in the art, during the synthesis of the alumina gel or by impregnation of the substrate used for the preparation of the catalyst according to the invention.

In an even more preferred manner, the porous oxide substrate that for the most part is calcined aluminum consists of alumina.

In a preferred manner, the alumina that is present in said substrate is a transition alumina such as a gamma-, delta-, theta-, chi-, rho- or eta-alumina, by itself or in a mixture. In a more preferred manner, the alumina is a gamma, delta, or theta transition alumina, by itself or in a mixture.

The following characteristics of the substrate correspond to the characteristics of the substrate that is used for the preparation of the catalyst according to the invention before impregnation of the active phase.

The substrate that is used for the preparation of the catalyst according to the invention has a total pore volume of at least 0.42 mL/g, preferably between 0.45 and 1.3 mL/g, and in a particularly preferred manner between 0.48 and 1.2 mL/g.

The substrate that is used for the preparation of the catalyst according to the invention advantageously has a macropore volume of between 5 and 40% of the total pore volume of the substrate, preferably between 8 and 35% of the total pore volume of the substrate, and in an even more preferred manner between 10 and 30% of the total pore volume of the substrate.

The mesopore volume of the substrate that is used for the preparation of the catalyst according to the invention is at least 0.40 mL/g, preferably between 0.45 and 1.2 mL/g, and in a particularly preferred manner between 0.45 and 1.0 mL/g.

The substrate that is used for the preparation of the catalyst according to the invention advantageously has a pore volume of the pores that have a pore diameter of between 100 and 700 nm that is less than 20% of the total pore volume of the substrate, preferably less than 18% of the total pore volume of the substrate, and in a particularly preferred manner less than 15% of the total pore volume of the substrate.

The median mesopore diameter of the substrate that is used for the preparation of the catalyst according to the invention is between 14 nm and 30 nm, and preferably between 16 and 28 nm, and in a particularly preferred manner between 18 and 25 nm.

The substrate that is used for the preparation of the catalyst according to the invention has a median macropore diameter of between 50 and 200 nm, preferably between 80 and 190 nm, and in an even more preferred manner between 90 and 180 nm.

The substrate that is used for the preparation of the catalyst according to the invention has a B.E.T. specific surface area of at least 40 m²/g, preferably at least 50 m²/g, and in an even more preferred manner between 60 and 400 m²/g.

When it is desired to use the catalyst according to the invention in a reaction for selective hydrogenation of polyunsaturated molecules such as diolefins, acetylenic compounds or alkenylaromatic compounds, the substrate that is used for the preparation of the catalyst according to the invention advantageously has a B.E.T. specific surface area of between 60 and 230 m²/g.

When it is desired to use the catalyst according to the invention in a reaction for hydrogenation of aromatic compounds, the substrate that is used for the preparation of the catalyst according to the invention advantageously has a B.E.T. specific surface area of between 130 and 400 m²/g.

Preferably, the substrate that is used for the preparation of the catalyst according to the invention has little microporosity; in a very preferred manner, it does not have any microporosity.

Characteristics of the Catalyst

The finished catalyst, i.e., with the active phase deposited on the substrate by any method that is known to one skilled in the art, as is described below, consequently has the textural properties given below.

The catalyst according to the invention has a total pore volume of at least 0.42 mL/g, preferably at least 0.45 mL/g, and in a particularly preferred manner between 0.48 and 1.0 mL/g.

The catalyst according to the invention advantageously has a macropore volume of between 5 and 40% of the total pore volume of the catalyst, preferably between 8 and 35% of the total pore volume of the catalyst, and in an even more preferred manner between 10 and 30% of the total pore volume of the catalyst.

The mesopore volume of the catalyst is at least 0.40 mL/g, preferably at least 0.45 mL/g, and in a particularly preferred manner between 0.45 mL/g and 0.8 mL/g.

The median mesopore diameter of the catalyst is between 14 nm and 30 nm, and preferably between 15 and 28 nm, and in a particularly preferred manner between 17 and 25 nm.

The catalyst has a median macropore diameter of between 50 and 200 nm, preferably between 80 and 190 nm, and in an even more preferred manner between 90 and 180 nm.

The catalyst according to this invention has a B.E.T. specific surface area of at least 40 m²/g, preferably at least 50 m²/g, and in an even more preferred manner between 55 and 250 m²/g.

When it is desired to use the catalyst according to the invention in a reaction for selective hydrogenation of polyunsaturated molecules such as diolefins, acetylenic compounds or alkenylaromatic compounds, the catalyst according to the invention advantageously has a B.E.T. specific surface area of between 55 and 170 m²/g.

When it is desired to use the catalyst according to the invention in a reaction for hydrogenation of aromatic compounds, the catalyst according to the invention advantageously has a B.E.T. specific surface area of between 90 and 250 m²/g.

Preferably, the catalyst has little microporosity; in a very preferred manner, it does not have any microporosity.

The nickel content is between 5 and 65% by weight of said element in relation to the total mass of the catalyst, preferably between 8 and 55% by weight, in an even more preferred manner between 10 and 40% by weight, and in a particularly preferred manner between 10 and 34% by weight. The Ni content is measured by X fluorescence.

When it is desired to use the catalyst according to the invention in a reaction for selective hydrogenation of polyunsaturated molecules such as diolefins, acetylenic compounds or alkenylaromatic compounds, the nickel content is advantageously between 5 and 25% by weight, preferably between 8 and 25% by weight, and more preferably between 10 and 23% by weight of said element in relation to the total mass of the catalyst.

When it is desired to use the catalyst according to the invention in a reaction for hydrogenation of aromatic compounds, the nickel content is advantageously between 15 and 65% by weight, preferably between 18 and 55% by weight, and more preferably between 19 and 34% by weight of said element in relation to the total mass of the catalyst.

The size of the nickel particles in the catalyst according to the invention is less than 20 nm, preferably between 1.5 and 18 nm. The diameter of the nickel crystallites in oxide form is understood by “size of the nickel particles.” The diameter of the nickel crystallites in oxide form is determined by X-ray diffraction, starting from the width of the diffraction line located at the 2theta angle=43° (i.e., in the crystallographic direction [200]), using the Scherrer equation. This method, which is used in X-ray diffraction on polycrystalline powders or samples and which connects the width at mid-height of the diffraction peaks to the size of the particles, is described in detail in the reference: Appl. Cryst. (1978), 11, 102-113 “Scherrer After Sixty Years: A Survey and Some New Results in the Determination of Crystallite Size,” J. I. Langford and A. J. C. Wilson.

The active phase of the catalyst can also comprise at least one additional metal that is selected from among the metals of group VIII, the metals of group IB, and/or tin. In a preferred manner, the additional metal of group VIII is selected from among platinum, ruthenium, and rhodium, as well as palladium. Advantageously, the additional metal of group IB is selected from among copper, gold, and silver. Said additional metal(s) of group VIII and/or group IB is (are) preferably present with a content representing 0.01 to 20% by weight of the mass of the catalyst, preferably 0.05 to 10% by weight of the mass of the catalyst, and in an even more preferred manner 0.05 to 5% by weight of the mass of said catalyst. Tin is preferably present with a content that represents 0.02 to 15% by weight of the mass of the catalyst, in such a way that the Sn/Ni molar ratio is between 0.01 and 0.2, preferably between 0.025 to 0.055, and in an even more preferred manner between 0.03 to 0.05.

The active phase of the catalyst does not comprise metal from group VIB. It does not comprise in particular molybdenum or tungsten.

Said catalyst according to the invention is generally presented in all of the forms known by one skilled in the art, for example in the form of balls (generally having a diameter of between 1 and 6 mm), extrudates, tablets, hollow cylinders. Preferably, it consists of extrudates with a diameter that is generally between 0.5 and 10 mm, preferably between 0.8 and 3.2 mm, and in a very preferred manner between 1.0 and 2.5 mm. The former can advantageously be presented in the form of extrudates that are cylindrical, multilobed, trilobed or quadrilobed. Preferably, its shape will be trilobed or quadrilobed. The shape of the lobes can be adjusted according to all of the methods known from the prior art.

Preparation Method

This invention also has as its object a method for preparation of said catalyst according to the invention.

The catalyst according to the invention is prepared from a specific alumina gel. The particular pore distribution that is observed in the catalyst is in particular due to the method for preparation starting from the specific alumina gel.

The method for preparation of the alumina gel comprises a first precipitation step, a heating step, a second precipitation step, and a filtering step. The gel is then subjected to a drying step so as to obtain a powder. The powder is then subjected to a heat treatment and then shaped so as to obtain a calcined aluminum porous oxide substrate. The calcined aluminum porous oxide substrate is then impregnated with a solution that comprises the salt(s) of the precursor(s) of the active phase, and then dried to obtain a dried catalyst. Then, the dried catalyst is optionally subjected to a heat treatment, and then generally reduced and subjected to a passivation treatment.

More particularly, the method for preparation of the catalyst according to the invention comprises the following steps:

-   -   a) A first precipitation step, in an aqueous reaction medium, of         at least one basic precursor that is selected from among sodium         aluminate, potassium aluminate, ammonia, sodium hydroxide, and         potassium hydroxide, and at least one acid precursor that is         selected from among aluminum sulfate, aluminum chloride,         aluminum nitrate, sulfuric acid, hydrochloric acid, and nitric         acid, in which at least one of the basic or acid precursors         comprises aluminum; the relative flow rate of the acid and basic         precursors is selected in such a way as to obtain a pH of the         reaction medium of between 8.5 and 10.5; and the flow rate of         the acid and basic precursors that contain aluminum is regulated         in such a way as to obtain a rate of advance of the first step         of between 5 and 13%, with the rate of advance being defined as         being the proportion of alumina that is formed into an         equivalent of Al₂O₃ during said first precipitation step in         relation to the total quantity of alumina that is formed into an         equivalent of Al₂O₃ at the end of step c) of the preparation         method, with said step being performed at a temperature of         between 20 and 90° C. and for a period of between 2 and 30         minutes,     -   b) A step of heating the suspension that is obtained in step a)         to a temperature of between 40 and 90° C. for a period of         between 7 and 45 minutes to obtain an alumina gel,     -   c) A second step for precipitation of the suspension that is         obtained at the end of step b) of heating by adding into the         suspension at least one basic precursor that is selected from         among sodium aluminate, potassium aluminate, ammonia, sodium         hydroxide, and potassium hydroxide, and at least one acid         precursor that is selected from among aluminum sulfate, aluminum         chloride, aluminum nitrate, sulfuric acid, hydrochloric acid,         and nitric acid, in which at least one of the basic or acid         precursors comprises aluminum; the relative flow rate of the         acid and basic precursors is selected in such a way as to obtain         a pH of the reaction medium of between 8.5 and 10.5; and the         flow rate of the acid and basic precursor(s) containing aluminum         is regulated in such a manner as to obtain a rate of advance of         the second step of between 87 and 95%, with the rate of advance         being defined as being the proportion of alumina that is formed         into an equivalent of Al₂O₃ during said second precipitation         step in relation to the total quantity of alumina that is formed         into an equivalent of Al₂O₃ at the end of step c) of the         preparation method, with said step being performed at a         temperature of between 40 and 90° C. and for a period of between         2 and 50 minutes,     -   d) A step for filtering the suspension that is obtained at the         end of step c) of second precipitation for obtaining an alumina         gel,     -   e) A step for drying said alumina gel that is obtained in         step d) for obtaining a powder,     -   f) A step for heat treatment at a temperature of between 500 and         1000° C., with or without the presence of an air stream         containing up to 60% by volume of water,     -   g) A shaping step for obtaining an aluminum porous oxide         substrate,     -   h) A step for impregnating said substrate with a solution that         comprises the salt(s) of the precursor(s) of the nickel-based         active phase,     -   i) A step for drying said impregnated substrate at a temperature         of between 15 and less than 250° C., in such a way as to obtain         a dried catalyst,     -   j) Optionally a heat treatment of said dried catalyst at a         temperature of between 250 and 1000° C. with or without the         presence of water.

Step a) First Precipitation

This step consists in bringing into contact, in an aqueous reaction medium, at least one basic precursor that is selected from among sodium aluminate, potassium aluminate, ammonia, sodium hydroxide, and potassium hydroxide, and at least one acid precursor that is selected from among aluminum sulfate, aluminum chloride, aluminum nitrate, sulfuric acid, hydrochloric acid, and nitric acid, in which at least one of the basic or acid precursors comprises aluminum; the relative flow rate of the acid and basic precursors is selected in such a way as to obtain a pH of the reaction medium of between 8.5 and 10.5, and the flow rate of the acid and basic precursor(s) containing aluminum is regulated in such a way as to obtain a rate of advance of the first step of between 5 and 13%, with the rate of advance being defined as being the proportion of alumina that is formed into an equivalent of Al₂O₃ during said first precipitation step in relation to the total quantity of alumina that is formed into an equivalent of Al₂O₃ at the end of step c) of the preparation method, with said step being performed at a temperature of between 20 and 90° C., and for a period of between 2 and 30 minutes.

The mixture in the aqueous reaction medium of at least one basic precursor and at least one acid precursor requires that at least one of the acid or basic precursors comprises aluminum. It is also possible that at least two of the basic and acid precursors comprise aluminum.

The basic precursors that comprise aluminum are sodium aluminate and potassium aluminate. The preferred basic precursor is sodium aluminate. The acid precursors that comprise aluminum are aluminum sulfate, aluminum chloride, and aluminum nitrate. The preferred acid precursor is aluminum sulfate.

In accordance with the invention, the acid precursors of alumina and the basic precursors of alumina can be used by themselves or in a mixture in the precipitation step.

Preferably, the basic and acid precursor(s) are added in said first precipitation step a) in an aqueous solution. Preferably, the aqueous reaction medium is water. Preferably, said step a) is performed while being stirred. Preferably, said step a) is carried out in the absence of an organic additive.

In accordance with the invention, the relative flow rate of the acid and basic precursors that they may or may not contain from aluminum is selected in such a way as to obtain a pH of the reaction medium of between 8.5 and 10.5, preferably between 8.5 and 10, and in a very preferred manner between 8.7 and 9.9.

In the preferred case where the basic and acid precursors are respectively sodium aluminate and aluminum sulfate, the ratio by mass of said basic precursor to said acid precursor is advantageously between 1.60 and 2.05. For the other basic and acid precursors, whether they contain aluminum or not, the base/acid ratios by mass are established by a curve of neutralization of the base by the acid. Such a curve is easily obtained by one skilled in the art.

The first precipitation step a) is carried out at a temperature of between 20 and 90° C., in a preferred manner between 20 and 70° C., and in a more preferred manner between 30 and 50° C.

The first precipitation step a) is carried out for a period of between 2 and 30 minutes, preferably between 5 and 20 minutes, and in a particularly preferred manner between 5 to 15 minutes.

According to the invention, the rate of advance of said first precipitation step a) is between 5 and 13%, preferably between 6 and 12%, and preferably between 7 and 11%. The rate of advance for each of the precipitation steps is defined as being the proportion of alumina that is formed into an equivalent of Al₂O₃ during said first or second [sic] of precipitation in relation to the total quantity of alumina that is formed into an equivalent of Al₂O₃ at the end of the two precipitation steps and more generally at the end of the steps for preparation of the alumina gel and in particular at the end of step c) of the preparation method according to the invention.

The acid and basic precursors that contain aluminum are therefore introduced in quantities that make it possible to obtain a suspension that contains the desired quantity of alumina, based on the final concentration of alumina that is to be attained.

Step b) Heating

In accordance with the invention, said preparation method comprises a step b) for heating the suspension that is obtained in step a) at a temperature of between 40 and 90° C. for a period of between 7 and 45 minutes to obtain an alumina gel.

Said step for heating the suspension that is obtained at the end of step a), implemented between said step a) of first precipitation and step c) of second precipitation, is performed at a temperature of between 40 and 90° C., preferably between 40 and 80° C., and in a preferred manner between 40 and 70° C.

Said heating step is implemented for a period of between 7 and 45 minutes, and preferably between 7 and 35 minutes.

Said heating step is advantageously implemented according to all of the heating methods that are known to one skilled in the art.

Step c) Second Precipitation

According to the invention, said preparation method comprises a second step for precipitation of the heating suspension that is obtained at the end of step b) of heating, with said second step being performed by adding into said suspension an aqueous solution of at least one basic precursor that is selected from among sodium aluminate, potassium aluminate, ammonia, sodium hydroxide, and potassium hydroxide, and at least one acid precursor that is selected from among aluminum sulfate, aluminum chloride, aluminum nitrate, sulfuric acid, hydrochloric acid, and nitric acid, in which at least one of the basic or acid precursors comprises aluminum, the relative flow rate of the acid and basic precursors is selected in such a way as to obtain a pH of the reaction medium of between 8.5 and 10.5, and the flow rate of the acid and basic precursor(s) containing aluminum is regulated in such a way as to obtain a rate of advance of the second step of between 87 and 95%, with the rate of advance being defined as being the proportion of alumina that is formed into an equivalent of Al₂O₃ during said second precipitation step in relation to the total quantity of alumina that is formed into an equivalent of Al₂O₃ at the end of step c) of the preparation method, with said step being performed at a temperature of between 40 and 90° C., and for a period of between 2 and 50 minutes.

Just as in the first precipitation step a), the addition into the heated suspension of at least one basic precursor and at least one acid precursor requires that at least one of the basic or acid precursors comprises aluminum. It is also possible that at least two of the basic and acid precursors comprise aluminum.

The basic precursors that comprise aluminum are sodium aluminate and potassium aluminate. The preferred basic precursor is sodium aluminate. The acid precursors that comprise aluminum are aluminum sulfate, aluminum chloride, and aluminum nitrate. The preferred acid precursor is aluminum sulfate.

Preferably, the basic and acid precursor(s) is/are added in step c) into aqueous solution. Preferably, the aqueous reaction medium is water. Preferably, said step c) is performed while being stirred. Preferably, said step c) is carried out in the absence of an organic additive.

Just as in step a) of precipitation, the relative flow rate of the acid and basic precursors, whether they contain aluminum or not, is selected in such a way as to obtain a pH of the reaction medium of between 8.5 and 10.5, preferably between 8.5 and 10, and in an even more preferred manner of between 8.7 and 9.9.

In the preferred case where the basic and acid precursors are respectively sodium aluminate and aluminum sulfate, the ratio by mass of said basic precursor to said acid precursor is advantageously between 1.60 and 2.05. For the other basic and acid precursors, whether they contain aluminum or not, the base/acid ratios by mass are established by a curve of neutralization of the base by the acid. Such a curve is easily obtained by one skilled in the art.

The second precipitation step is carried out at a temperature of between 40 and 90° C., preferably between 40 and 80° C., in a preferred manner between 45 and 70° C., and in a very preferred manner between 50 and 70° C.

The second precipitation step is carried out for a period of between 2 and 50 minutes, preferably between 5 and 45 minutes, and in a preferred manner between 7 to 40 minutes.

The aluminum precursors are also mixed in quantities that make it possible to obtain a suspension that contains the desired quantity of alumina, based on the final concentration of alumina to be attained. In particular, said second precipitation step makes it possible to obtain 87 to 95% by weight of alumina in relation to the total quantity of alumina that is formed at the end of the two precipitation steps.

Just as in the precipitation step a), the flow rate of the acid and basic precursor(s) containing aluminum is regulated in such a way as to obtain a rate of advance of the second step of between 87 and 95%, preferably between 88 and 94%, in a very preferred manner between 89 and 93%. The rate of advance for each of the precipitation steps is defined as being the proportion of alumina that is formed into an equivalent of Al₂O₃ during said first or second [sic] of precipitation in relation to the total quantity of alumina that is formed into an equivalent of Al₂O₃ at the end of the two precipitation steps and more generally at the end of the steps for preparation of the alumina gel and in particular at the end of step c) of the preparation method according to the invention.

Thus, based on the alumina concentration set as the target at the end of the two steps a) and c) of precipitation, generally between 20 and 100 g/L, preferably between 20 and 80 g/L, in a preferred manner between 20 and 50 g/L, the quantities of aluminum that have to be provided by the acid and/or basic precursors are calculated, and the flow rate of the precursors is regulated based on the concentration of said added aluminum precursors, the quantity of water added into the reaction medium, and the rate of advance required for each of the precipitation steps.

Just as in the precipitation step a), the flow rates of the acid and/or basic precursor(s) that contain aluminum depend on the size of the reactor that is used and thus on the quantity of water added in the reaction medium.

By way of example, if work is done in a 3-L reactor and if 1 L of alumina suspension with a final concentration of Al₂O₃ of 50 g/L is set as the target, with a targeted rate of advance of 10% for the first precipitation step, 10% of the total alumina is to be provided during step a) of precipitation. The alumina precursors are sodium aluminate at a concentration of 155 g/L of Al₂O₃ and aluminum sulfate at a concentration of 102 g/L of Al₂O₃. The pH of precipitation of the first step is set at 9.5, and the second at 9. The quantity of water added into the reactor is 620 mL.

For the first step a) of precipitation being performed at 30° C. and for 8 minutes, the aluminum sulfate flow rate is to be 2.1 mL/minute, and the sodium aluminate flow rate is 2.6 mL/minute. The ratio by mass of sodium aluminate to the aluminum sulfate is therefore 1.91.

For the second precipitation step, being performed at 70° C., for 30 minutes, the flow rate of aluminum sulfate is to be 5.2 mL/minute, and the flow rate of sodium aluminate is 6.3 mL/minute. The ratio by mass of sodium aluminate to aluminum sulfate is therefore 1.84.

Step d) Filtering

The method for preparation of alumina according to the invention also comprises a step for filtering the suspension that is obtained at the end of step c) of second precipitation in such a way as to obtain an alumina gel. Said filtering step is carried out according to the methods that are known to one skilled in the art.

Said filtering step is advantageously followed by at least one washing step, preferably with water and preferably with one to three washing steps, with a quantity of water that is equal to the quantity of filtered precipitate.

The filterability of the suspension that is obtained at the end of the two precipitation steps is improved by the low dispersibility of the alumina gel obtained, which makes it possible to improve the productivity of the method according to the invention as well as to make possible an extrapolation of the method on the industrial level. The dispersibility is defined as the weight of peptized alumina gel or solid that cannot be dispersed by centrifuging in a polypropylene tube at 3600 G for 3 minutes.

At the end of step d), an alumina gel, also called boehmite, is obtained, which gel has a dispersibility rate that is less than or equal to 15%, preferably between 5 and 15%, and in a preferred manner between 6 and 14%, and in a very preferred manner of between 7 and 13%, and in an even more preferred manner between 7 and 10%, and a boehmite particle size of between 1 and 35 nm and preferably between 2 to 35 nm.

The low dispersibility rate of the thus prepared gel makes it possible to facilitate the step of shaping said gel according to all of the methods that are known to one skilled in the art and in particular by mixing-extrusion, by granulation, by pelletizing, and by the so-called oil-drop technique (draining).

Step e) Drying of Alumina Gel

In accordance with the invention, the alumina gel that is obtained at the end of step c) of second precipitation, followed by a step d) of filtering, is dried in a step e) of drying for obtaining a powder. Said drying step is generally implemented by drying at a temperature of between 20 and 200° C. and for a period of between 8 and 15 hours, or by atomization or by any other drying technique known to one skilled in the art.

In the case where said step e) of drying is implemented by atomization, the “cake” obtained at the end of the second precipitation step, followed by a filtering step, is resuspended. Said suspension is then sprayed in fine droplets, into a vertical cylindrical chamber in contact with a hot air current so as to evaporate the water according to the principle that is well known to one skilled in the art. The powder that is obtained is entrained by the heat stream until it reaches a cyclone or a sleeve filter that will separate the air from the powder.

Preferably, in the case where said step e) of drying is implemented by atomization, the atomization is carried out according to the operating procedure described in the publication Asep Bayu Dani Nandiyanto, Kikuo Okuyama, Advanced Powder Technology, 22, 1-19, 2011.

Step f) Heat Treatment

In accordance with the invention, a heat treatment step is then carried out at a temperature of between 500 and 1000° C., with or without the presence of an air stream containing up to 60% by volume of water.

Preferably, said step f) of heat treatment is performed at a temperature of between 540 and 850° C. Preferably, said step f) of heat treatment is performed for a period of between 2 and 10 hours.

“Heat treatment” is defined as the temperature treatment respectively without the presence or with the presence of water. In this latter case, the contact with water vapor can take place at atmospheric pressure (“steaming”) or with autogenous pressure (autoclaving). Multiple cycles combined without the presence or with the presence of water can be carried out.

In the case of the presence of water, the water content is preferably between 150 and 900 grams per kilogram of dry air, and, in an even more preferred manner, between 250 and 650 grams per kilogram of dry air.

Said step f) of heat treatment makes possible the transition of alumina gel, also called boehmite, to a calcined alumina. The alumina has a crystallographic structure of a transition alumina such as gamma, delta, theta, chi, rho or eta, by itself or in a mixture. In a more preferred manner, the alumina is a gamma, delta or theta transition alumina, by itself or in a mixture. The existence of the different crystallographic structures is linked to the conditions of implementing step f) of heat treatment.

Step g) Shaping

A shaping step for obtaining an aluminum porous oxide substrate is then carried out.

Preferably, said step g) of shaping is carried out according to any technique that is known to one skilled in the art, for example the methods of shaping by extrusion, by pelletization, by the oil-drop method (draining), or by turntable granulation.

In a very preferred manner, said step g) of shaping is carried out by extrusion. It is possible to use a piston extruder through a die that has the desired diameter, typically between 0.5 and 10 mm. The extrudates generally have a diameter of between 0.5 and 10 mm, preferably 0.8 and 3.2 mm, and in a very preferred manner between 1.0 and 2.5 mm. The extrudates can advantageously be presented in the form of extrudates that are cylindrical, multilobed, trilobed, or quadrilobed. Preferably, the shape will be trilobed or quadrilobed.

Any other element, for example silica in the form of a solution or an emulsion of silicic precursor, can be introduced during the shaping.

Step h) Impregnation of the Active Phase

According to step h) of the method according to the invention, the calcined aluminum porous oxide substrate is impregnated with a solution that comprises the salt(s) of the precursor(s) of the nickel-based active phase.

The active phase is provided by one or more solutions that contain at least nickel.

Said solution(s) can be aqueous or consist of an organic solvent or else a mixture of water and at least one organic solvent (for example, ethanol or toluene). Preferably, the solution is aqueous. The pH of this solution can be modified by the optional addition of an acid. According to another preferred variant, the aqueous solution can contain ammonia or NH₄ ⁺ ammonium ions.

In a preferred manner, said nickel precursor is introduced into aqueous solution, for example in the form of nitrate, carbonate, acetate, chloride, hydroxide, hydroxycarbonate, oxalate, complexes formed by a polyacid or an acid-alcohol and its salts, complexes formed with the acetylacetonates, or any other inorganic derivative that is soluble in aqueous solution, which is brought into contact with said calcined aluminum porous oxide. In a preferred manner, nickel nitrate, nickel chloride, nickel acetate or nickel hydroxycarbonate is advantageously used as a nickel precursor. In a very preferred manner, the nickel precursor is nickel nitrate or nickel hydroxycarbonate.

According to another preferred variant, said nickel precursor is introduced into ammoniacal solution by introducing a nickel salt, for example nickel hydroxide or nickel carbonate in an ammoniacal solution or in a solution of ammonium carbonate or ammonium bicarbonate.

The quantities of the nickel precursor(s) introduced into the solution are selected in such a way that the total nickel content is between 5 and 65% by weight, preferably between 8 and 55% by weight, in a preferred manner between 10 and 40% by weight, and in a particularly preferred manner between 10 and 34% by weight of said element in relation to the total mass of the catalyst. The nickel contents are generally adapted to the targeted hydrogenation reaction as described above in the paragraph of the description of the catalyst.

Any other additional element can be introduced at the time of this step:

When it is desired to introduce phosphorus, a phosphoric acid solution can be introduced into the impregnation solution.

When it is desired to introduce an additional metal that is selected from among the metals of group VIII, the metals of group IB and/or tin, a salt that is selected from among nitrate, sulfate, chloride or any other conventional precursor is advantageously used as a precursor.

An additive, for example a chelating agent of organic nature, can advantageously be introduced into the solution if one skilled in the art deems it necessary.

The impregnation of the active phase can be carried out according to all of the methods that are known to one skilled in the art, in particular by dry impregnation. In a preferred way, nickel, and optionally at least one supplementary element such as an additional metal that is selected from among the metals of group VIII, the metals of group IB, and/or tin, phosphorus, or an additive such as a chelating agent of an organic nature are deposited by dry impregnation of their associated precursors on the oxide substrate according to the invention.

The deposition can be done via a single dry impregnation step of the oxide substrate according to the invention via the use of a solution that simultaneously contains at least one nickel compound, and optionally at least one supplementary element.

The deposition can also advantageously be done via at least two dry impregnation cycles. The different elements can thus be advantageously successively impregnated or else one of the elements can also be impregnated in multiple sequences. One of the impregnations that is carried out can make it possible in particular to introduce an organic compound in addition to the active phase of the catalyst. In these cases, each impregnation is advantageously followed by drying and optionally a heat treatment. The drying can be done at a temperature of between 15 and 250° C., preferably between 80 and 200° C., generally for a period of between 10 minutes and 24 hours. The heat treatment can be done at a temperature of between 200 and 1000° C., preferably between 250 and 750° C., generally for a period of between 15 minutes and 10 hours.

Step i) Drying of the Impregnated Substrate

In accordance with the invention, the impregnated substrate that is obtained at the end of step h) of impregnation of the active phase undergoes a step i) of drying at a temperature of between 15 and less than 250° C., preferably between 80 and 200° C., according to any technique that is known to one skilled in the art, for a period that is typically between 10 minutes and 24 hours. A dried catalyst is obtained.

Step j) Heat Treatment of the Dried Catalyst

The thus dried catalyst can then undergo a complementary step j) of heat treatment at a temperature of between 250 and 1000° C. and preferably between 250 and 750° C., for a period that is typically between 15 minutes and 10 hours, with or without the presence of water.

“Heat treatment” is defined as the temperature treatment respectively without or with the presence of water. In this latter case, the contact with the water vapor can take place at atmospheric pressure (“steaming”) or under autogenous pressure (autoclaving). Multiple combined cycles of hydrothermal or heat treatments can be carried out. After this or these treatment(s), the catalyst precursor comprises nickel in oxide form, i.e., in NiO form.

In the case of hydrothermal treatment, the water content is preferably between 150 and 900 grams per kilogram of dry air, and in an even more preferred manner, between 250 and 650 grams per kilogram of dry air.

Step k) Reduction by a Reducing Gas

Prior to the use of the catalyst in the catalytic reactor and the implementation of a hydrogenation method, at least one step k) of reducing treatment is advantageously carried out in the presence of a reducing gas after steps i) or j) in such a way as to obtain a catalyst that comprises nickel that is at least partially in metallic form.

This treatment makes it possible to activate said catalyst and to form metal particles, in particular nickel in the zero-valent state. Said reducing treatment can be carried out in-situ or ex-situ, i.e., after or before the loading of the catalyst into the hydrogenation reactor. Said step k) of reducing treatment can be implemented on the catalyst that may or may not have been subjected to step l) of passivation, described below.

The reducing gas is preferably hydrogen. The hydrogen can be used in pure form or in a mixture (for example, a mixture of hydrogen/nitrogen, hydrogen/argon, hydrogen/methane). In the case where hydrogen is used in a mixture, all of the proportions can be considered.

Said reducing treatment is carried out at a temperature of between 120 and 500° C., preferably between 150 and 450° C. When the catalyst does not undergo passivation or undergoes a reducing treatment before passivation, the reducing treatment is carried out at a temperature of between 350 and 500° C., preferably between 350 and 450° C. When the catalyst has undergone passivation in advance, the reducing treatment is generally carried out at a temperature of between 120 and 350° C., preferably between 150 and 350° C.

The duration of the reducing treatment is generally between 2 and 40 hours, preferably between 3 and 30 hours. The rise in temperature to the desired reduction temperature is generally slow, for example set between 0.1 and 10° C./minute, preferably between 0.3 and 7° C./minute.

The flow rate of hydrogen, expressed in terms of L/hour/gram of catalyst, is between 0.1 and 100 L/hour/gram of catalyst, preferably between 0.5 and 10 L/hour/gram of catalyst, in an even more preferred way between 0.7 and 5 L/hour/gram of catalyst.

Step l) Passivation

Prior to its implementation in the catalytic reactor, the catalyst according to the invention can optionally undergo a passivation step (step l) by a sulfur-containing compound or an oxidized compound or by the CO₂ before or after step k) of reducing treatment. This passivation step can be carried out ex-situ or in-situ. The passivation step is carried out by the implementation of methods that are known to one skilled in the art.

The sulfur passivation step makes it possible to improve the selectivity of catalysts and to prevent heat excursions during start-ups of new catalysts (“run away” according to English terminology). The passivation generally consists in irreversibly poisoning, by the sulfur-containing compound, the most virulent active sites of nickel that exist in the new catalyst and therefore in minimizing the activity of the catalyst to benefit its selectivity. The passivation step is carried out by implementing methods that are known to one skilled in the art and in particular, by way of example, by implementing one of the methods described in the documents of patents EP0466567, U.S. Pat. No. 5,153,163, FR2676184, WO2004/098774, EP0707890. The sulfur-containing compound is selected from among, for example, the following compounds: thiophene, thiophane, alkyl monosulfides such as dimethyl sulfide, diethyl sulfide, dipropyl sulfide, and propyl methyl sulfide or else an organic disulfide of formula HO—R₁—S—S—R₂—OH such as the di-thio-di-ethanol of formula HO—C₂H₄—S—S—C₂H₄—OH (often called DEODS). The sulfur content is generally between 0.1 and 2% by weight of said element in relation to the mass of the catalyst.

The step of passivation by an oxidized compound or by CO₂ is generally carried out after a reducing treatment in advance at a high temperature, generally between 350 and 500° C., and it makes it possible to preserve the metal phase of the catalyst in the presence of air. A second reducing treatment at a lower temperature generally between 120 and 350° C. is then generally performed. The oxidized compound is generally air or any other stream that contains oxygen.

Selective Hydrogenation Method

This invention also relates to the use of the catalyst according to the invention in a hydrogenation method and in particular in a method for selective hydrogenation of polyunsaturated molecules such as diolefins, acetylenic compounds, or alkenylaromatic compounds, also called styrene compounds.

The mono-unsaturated organic compounds, such as, for example, ethylene and propylene, are at the source of the manufacturing of polymers, plastic materials, and other value-added chemical products. These compounds are obtained from natural gas, naphtha, or diesel fuel, which have been treated by steam-cracking or catalytic-cracking methods. These methods are performed at high temperature and produce, in addition to desired mono-unsaturated compounds, polyunsaturated organic compounds such as acetylene, propadiene, and methylacetylene (or propyne), 1,2-butadiene, and 1,3-butadiene, vinylacetylene, and ethylacetylene, and other polyunsaturated compounds whose boiling point corresponds to the C5+ gasoline fraction (gasolines that contain hydrocarbon compounds that have 5 or more carbon atoms), in particular diolefinic or styrene or indene compounds. These polyunsaturated compounds are very reactive and lead to parasitic reactions in the polymerization units. It is therefore necessary to eliminate them before upgrading these fractions.

The selective hydrogenation is the main treatment that is developed for eliminating specifically the undesirable polyunsaturated compounds from these hydrocarbon feedstocks. It makes possible the conversion of polyunsaturated compounds to the corresponding alkenes or aromatic compounds by preventing their total saturation and therefore the formation of corresponding alkanes or naphthenes. In the case of steam-cracking gasolines used as feedstock, the selective hydrogenation also makes it possible to hydrogenate selectively the alkenylaromatic compounds into aromatic compounds by preventing the hydrogenation of the aromatic cores.

The hydrocarbon feedstock that is treated in the selective hydrogenation method has a final boiling point that is less than or equal to 250° C. and that contains at least 2 carbon atoms per molecule and comprises at least one polyunsaturated compound. “Polyunsaturated compounds” are defined as compounds that comprise at least one acetylene group and/or at least one diene group and/or at least one alkenylaromatic group.

More particularly, the feedstock is selected from the group that consists of a C2 steam-cracking fraction, a C3 steam-cracking fraction, a C4 steam-cracking fraction, a C5 steam-cracking fraction, and a steam-cracking gasoline that is also called pyrolysis gasoline. The steam-cracking gasoline or pyrolysis gasoline corresponds to a hydrocarbon fraction whose boiling point is generally between 0 and 250° C., preferably between 10 and 220° C. The polyunsaturated hydrocarbons that are to be hydrogenated and that are present in said steam-cracking gasoline are in particular diolefinic compounds (butadiene, isoprene, cyclopentadiene . . . ), styrene compounds (styrene, alpha-methylstyrene . . . ) and indene compounds (indene . . . ). The steam-cracking gasoline generally comprises the C5-C12 fraction with traces of C3, C4, C13, C14, C15 (for example, between 0.1 and 3% by weight for each of these fractions). For example, a feedstock that is formed from pyrolysis gasoline generally has the following composition: 5 to 25% by weight of paraffins, 40 to 70% by weight of aromatic compounds, 5 to 20% by weight of monoolefins, 5 to 40% by weight of diolefins, 1 to 10% by weight of alkenylaromatic compounds, and 20 to 300 ppm by weight of sulfur, with all of the compounds forming 100%. In a preferred manner, the polyunsaturated hydrocarbon feedstock that is treated in accordance with the selective hydrogenation method according to the invention is a steam-cracking gasoline.

The purpose of the selective hydrogenation method according to the invention is to eliminate said polyunsaturated hydrocarbons that are present in said feedstock to be hydrogenated without hydrogenating the monounsaturated hydrocarbons. For example, when said feedstock is a C2 fraction, the purpose of the selective hydrogenation method is to hydrogenate acetylene selectively. When said feedstock is a C3 fraction, the purpose of the selective hydrogenation method is to hydrogenate propadiene and methylacetylene selectively. In the case of a C4 fraction, the purpose is to eliminate butadiene, vinylacetylene (VAC), and butyne; in the case of a C5 fraction, the purpose is to eliminate the pentadienes. When said feedstock is a steam-cracking gasoline, the purpose of the selective hydrogenation method is to hydrogenate selectively said polyunsaturated hydrocarbons that are present in said feedstock to be treated in such a way that the diolefinic compounds are partially hydrogenated into monoolefins and the styrene and indene compounds are partially hydrogenated into corresponding aromatic compounds by preventing the hydrogenation of the aromatic cores.

The technological implementation of the selective hydrogenation method is carried out by, for example, injection, upward or downward flow, of the polyunsaturated hydrocarbon feedstock and hydrogen in at least one fixed-bed reactor. Said reactor can be of the isothermal type or of the adiabatic type. An adiabatic reactor is preferred. The polyunsaturated hydrocarbon feedstock can advantageously be diluted by one or more re-injection(s) of effluent, obtained from said reactor where the selective hydrogenation reaction occurs, at various points of the reactor, located between the inlet and the outlet of the reactor so as to limit the temperature gradient in the reactor. The technological implementation of the selective hydrogenation method according to the invention can also be advantageously carried out by the installation of at least said supported catalyst in a reactive distillation column or in reactors-exchangers. The hydrogen stream can be introduced at the same time as the feedstock that is to be hydrogenated and/or at one or more different points of the reactor.

The selective hydrogenation of the C2, C3, C4, C5 and C5+ fractions can be carried out in the gaseous phase or in the liquid phase, preferably in the liquid phase for the C3, C4, C5 and C5+ fractions. Actually, a liquid-phase reaction makes it possible to lower the energy cost and to increase the service life of the catalyst.

In a general manner, the selective hydrogenation is carried out at a temperature of between 0 and 500° C., at a pressure of between 0.1 and 20 MPa, at a hydrogen/(polyunsaturated compounds to be hydrogenated) molar ratio of between 0.1 and 10, and at an hourly volumetric flow V.V.H. (defined as the ratio of the volumetric flow rate of feedstock to the volume of catalyst) of between 0.1 and 200 h⁻¹ for a liquid feedstock, between 100 and 15000 h⁻¹ for a gaseous feedstock of a hydrocarbon feedstock that contains polyunsaturated compounds that contain at least 2 carbon atoms per molecule and that have a final boiling point that is less than or equal to 250° C.

In a preferred manner, a selective hydrogenation method is carried out in which the feedstock is a steam-cracking gasoline that comprises polyunsaturated compounds; the (hydrogen)/(polyunsaturated compounds to be hydrogenated) molar ratio is generally between 1 and 2; the temperature is generally between 40 and 200° C., preferably between 50 and 180° C.; the hourly volumetric flow rate (V.V.H.) is generally between 0.5 and 50 h⁻¹, preferably between 1 and 20 h⁻¹, and the pressure is generally between 0.3 and 6.5 MPa, preferably between 2.0 and 3.5 MPa. The hydrogen flow rate is adjusted so as to use a sufficient quantity of it theoretically to hydrogenate all of the polyunsaturated compounds and to maintain excess hydrogen at the reactor outlet.

Method for Hydrogenation of Aromatic Compounds

This invention also relates to the use of the catalyst according to the invention in a hydrogenation method and in particular in a method for hydrogenation of aromatic compounds making it possible to transform the aromatic compounds of petroleum or petrochemical fractions by conversion of aromatic cores into naphthene cores.

The hydrocarbon feedstock that is treated in the method for hydrogenation of aromatic compounds has a final boiling point that is less than or equal to 650° C., generally between 20 and 650° C., and preferably between 20 and 450° C., and it contains at least one aromatic or polyaromatic compound. As a petroleum or petrochemical fraction that contains aromatic compounds, it is possible to cite, for example, kerosene, light diesel fuel, heavy diesel fuel, and cracking distillates, such as FCC recycling oil, coking unit diesel fuel, hydrocracking distillates, and the reformate from catalytic reforming.

The content of aromatic hydrocarbons in a feedstock that is treated in the hydrogenation method is generally between 0.1 and 80% by weight, preferably between 1 and 50% by weight, and in a particularly preferred manner between 2 and 35% by weight, with the percentage by weight being based on the total weight of the hydrocarbon feedstock. The aromatic compounds that are present are, for example, benzene or alkylaromatic compounds such as toluene, ethylbenzene, o-xylene, m-xylene, or p-xylene, or else aromatic compounds that have multiple aromatic (polyaromatic) cores, such as naphthalene.

The sulfur or chlorine content of the feedstock is generally less than 5000 ppm by weight of sulfur or chlorine respectively, preferably less than 100 ppm by weight, and in a particularly preferred manner less than 10 ppm.

The technological implementation of the method for hydrogenation of aromatic compounds can be carried out like the one described in the selective hydrogenation part.

The hydrogenation of aromatic compounds can be carried out in the gaseous phase or in the liquid phase, preferably in the liquid phase. In a general manner, the hydrogenation of the aromatic compounds is performed at a temperature of between 30 and 350° C., preferably between 50 and 325° C., at a pressure of between 0.1 and 20 MPa, preferably between 0.5 and 10 MPa, at a hydrogen/(aromatic compounds to be hydrogenated) molar ratio of between 0.1 and 10, and at an hourly volumetric flow rate V.V.H. of between 0.05 and 50 h⁻¹, preferably between 0.1 and 10 h⁻¹ of a hydrocarbon feedstock that contains aromatic compounds and that has a final boiling point that is less than or equal to 650° C. The flow rate of hydrogen is adjusted so as to use a sufficient quantity of it theoretically to hydrogenate all of the polyunsaturated compounds and to maintain excess hydrogen at the reactor outlet.

The conversion of the aromatic or polyaromatic compounds is generally greater than 20 mol %, preferably greater than 40 mol %, in a more preferred manner greater than 80 mol %, and in a particularly preferred manner greater than 90 mol % of the aromatic or polyaromatic compounds that are contained in the hydrocarbon feedstock. The conversion is calculated by dividing the difference between the total moles of the aromatic or polyaromatic compounds in the hydrocarbon feedstock and in the product by the total moles of the aromatic or polyaromatic compounds in the hydrocarbon feedstock.

According to a particular variant, the catalyst according to the invention is used in a method for hydrogenation of a hydrocarbon feedstock that contains benzene, such as, for example, the reformate that is obtained from a catalytic reforming unit. The benzene content is generally between 0.1 and 40% by weight, preferably between 0.5 and 35% by weight, and in a particularly preferred manner between 2 and 30% by weight, with the percentage by weight being based on the total weight of the hydrocarbon feedstock.

The sulfur or chlorine content of the feedstock is generally less than 10 ppm by weight of sulfur or chlorine respectively, and preferably less than 2 ppm by weight.

The hydrogenation of the feedstock that contains benzene can be carried out in the gaseous phase or in the liquid phase, preferably in the liquid phase. When it is carried out in the liquid phase, a solvent can be present. In a general manner, the hydrogenation of benzene is carried out at a temperature of between 30 and 250° C., preferably between 50 and 200° C., and in a more preferred manner between 80 and 180° C., at a pressure of between 0.1 and 10 MPa, preferably between 0.5 and 4 MPa, with a hydrogen/(benzene) molar ratio of between 0.1 and 10, and at an hourly volumetric flow rate V.V.H. of between 0.05 and 50 h⁻¹, preferably between 0.5 and 10 h⁻¹.

The conversion of benzene is generally greater than 50 mol %, preferably greater than 80 mol %, in a more preferred manner greater than 90 mol %, and in a particularly preferred manner greater than 98 mol %.

The invention is illustrated by the following examples.

EXAMPLES Example 1 Preparation of an Aqueous Solution of Ni Precursors

The aqueous solution of Ni precursors (solution S) that is used for the preparation of catalysts A, B, and C is prepared by dissolving 46.1 g of nickel nitrate (NiNO₃, supplier Strem Chemicals®) in a volume of 13 mL of distilled water. The solution S whose NiO concentration is 20.1% by weight (in relation to the mass of the solution) is obtained.

Example 2 Preparation of a Catalyst A, According to the Invention

The catalyst A according to the invention is prepared by dry impregnation of the solution S of Ni precursors on an alumina A1. The goal is a content of 20% by weight of nickel in relation to the total mass of the catalyst.

The synthesis of alumina A1 according to the invention is carried out in a 5-L reactor in seven steps, named a) to g) below. The concentration of the acid and basic alumina precursors is as follows: aluminum sulfate Al₂(SO₄)₃ with 102 g/L of Al₂O₃ and sodium aluminate NaAlOO with 155 g/L of Al₂O₃. An attempt is made to obtain a final concentration of alumina of 45 g/L in the suspension that is obtained at the end of step c) of second precipitation.

-   -   a) A first precipitation of aluminum sulfate Al₂(SO₄)₃ and         sodium aluminate NaAlOO in 8 minutes at 30° C., pH=9.1, and with         a rate of advance of 10%. This rate of advance corresponds to         the proportion of alumina that is formed into an equivalent of         Al₂O₃ during this first step.     -   b) A rise in temperature of 30° C. to 70° C. in 20 to 30         minutes.     -   c) A second precipitation of aluminum sulfate Al₂(SO₄)₃ and         sodium aluminate NaAlOO in 30 minutes at 70° C., pH=9.1, and         with a rate of advance of 90%. This rate of advance corresponds         to the proportion of alumina that is formed into an equivalent         of Al₂O₃ during this second precipitation step.     -   d) A filtering of the suspension that is obtained at the end of         step c) by movement on a P4 sintered Buchner-type tool, followed         by three successive washing cycles with 5 L of distilled water.     -   e) A drying of alumina gel for one night at 120° C.     -   f) A heat treatment by calcination of dried alumina gel that is         obtained at the end of step e) under a stream of air of 1 L/h/g         of alumina at 750° C. for 2 hours (temperature rise slope of 5°         C./minute).     -   g) Shaping is done using a “Brabender”-type mixer with an acid         level of 1% (total acid level, expressed in relation to the dry         alumina), a neutralization rate of 20%, and acid and basic fire         losses respectively of 62% and 64%. Then, the extrusion is         carried out on a piston extruder through a trilobed die with a         2.1 mm diameter. After extrusion, the extrudates are dried for         one night at 80° C. The alumina A1 is obtained.

The characteristics of the alumina A1 thus obtained are recorded in Table 1 below.

The catalyst A is then prepared by dry impregnation of the solution S of Ni precursors, described in Example 1, on the alumina A1 according to the three steps, named h) to i) below:

-   -   h) A dry impregnation of the alumina Al by adding drop-by-drop a         volume of 11.5 mL of solution S to a mass of 10.5 g of alumina         A1, for a period of 10 minutes.     -   i) Drying of the catalytic precursor that is obtained at the end         of step h) in the oven at 120° C. for one night.     -   j) A heat treatment by calcination of the catalyst that is dried         under a stream of air of 1 L/h/g of catalyst, at 450° C. for 2         hours (temperature rise slope of 5° C./minute).

The calcined catalyst A is then obtained.

The characteristics of the calcined catalyst A that is thus obtained are recorded in Table 1 below.

TABLE 1 Properties of Catalysts A (According to the Invention) and B and C (For Comparison) ALUMINAS A1 B1 C1   According For For to the Com- Com- Invention parison parison B.E.T. Surface Area (m²/g) 139 180 298 Total Pore Volume (mL/g) 0.97 0.82 0.57 Mesopore Volume (mL/g) 0.75 0.63 0.55 Median Mespore Diameter (nm) 20.5 13.0 17 Macropore Volume (mL/g) 0.22 0.19 0 Macropore Volume (% of the 23 23 0 Total Pore Volume) Median Macropore Diameter 113 143 No (nm) Macro- porosity Pore volume of the pores that 0.13 0.12 0 have a pore diameter of between 100 and 700 nm (mL/g) Pore volume of the pores that 13 14.5 0 have a pore diameter of between 100 and 700 nm (% of the total pore volume) Micropore Volume (mL/g) 0 0 0 CATALYSTS A B C According For For to the Com- Com- Invention parison parison Ni (% by Weight) 20.5 19.4 21 B.E.T. Surface Area (m²/g) 106 119 206 Total Pore Volume (mL/g) 0.70 0.62 0.47 Mesopore Volume (mL/g) 0.54 0.48 0.47 Median Mesopore Diameter (nm) 18.5 10.5 10.5 Macropore Volume (mL/g) 0.16 0.14 0 Macropore Volume (% of the 23 23 0 Total Pore Volume) Median Macropore Diameter 112.5 132 No (nm) Macro- porosity Micropore Volume (mL/g) 0 0 0 Size of the NiO 16.5 14.1 11.0 Crystallites (nm)

Example 3 Preparation of Catalyst B that Has a Different Pore Distribution (For Comparison)

The catalyst B is prepared by dry impregnation of the solution S of Ni precursors by aiming at a content of 20% by weight of nickel in relation to the total mass of the catalyst on an alumina B1 that has a different pore distribution from that of the alumina A1 that is described in Example 2 above. The characteristics of this alumina B1 are recorded in Table 1. In particular, this alumina B1 has a median mesopore diameter that is much smaller than that of the alumina A1.

The catalyst B is then prepared by dry impregnation of the solution S of Ni precursors, described in Example 1, on the alumina B1 according to the three steps, steps h) to i), of Example 2 described above. The operating conditions are strictly identical. The calcined catalyst B is then obtained.

The characteristics of the calcined catalyst B that is thus obtained are recorded in Table 1. It has a median mesopore diameter that is much smaller than that of Catalyst A and NiO crystallites that are smaller than those of the catalyst A.

Example 4 Preparation of the Catalyst C that Has a Different Pore Distribution (For Comparison)

The catalyst C is prepared by dry impregnation of the solution S of Ni precursors by aiming at a content of 20% by weight of nickel in relation to the total mass of the catalyst on an alumina C1 that has a pore distribution that is also different from that of the alumina A1 that is described in Example 2 above. The characteristics of this alumina C1 are recorded in Table 1. In particular, this alumina C1 does not have macroporosity, and its median mesopore diameter is smaller than that of the alumina A1.

The catalyst C is then prepared by dry impregnation of the solution S of Ni precursors, described in Example 1, on the alumina C1. In this alumina of small pore volume, two successive impregnations have been necessary for reaching an Ni content of approximately 20% by weight; the linking of the three steps h) to i) of Example 2 described above was then repeated twice (according to the sequence h, i, j, h, i, j). The first impregnation step makes it possible to obtain a content of 13% by weight of nickel; the second impregnation step makes it possible to reach a content of 21% by weight of nickel in relation to the total mass of the catalyst. For each step, the operating conditions are strictly identical to those described in Example 2 above. The calcined catalyst C is then obtained.

The characteristics of the calcined catalyst C that is thus obtained are recorded in Table 1. This catalyst does not have macroporosity, and its median mesopore diameter is much smaller than that of the catalyst A. In addition, it has NiO crystallites that are smaller than those of the catalyst A.

Example 5 Evaluation of the Catalytic Properties of the Catalysts A, B and C with Regard to Selective Hydrogenation of a Mixture that Contains Styrene and Isoprene

The catalysts A, B and C that are described in the examples above are tested with regard to the reaction for selective hydrogenation of a mixture that contains styrene and isoprene.

The composition of the feedstock that is to be selectively hydrogenated is as follows: 8% by weight of styrene (supplier Sigma Aldrich®, purity 99%), 8% by weight of isoprene (supplier Sigma Aldrich®, purity 99%), 84% by weight of n-heptane (solvent) (supplier VWR®, purity>99% HPLC Chromanorm). This feedstock also contains sulfur-containing compounds of very low content: 10 ppm by weight of sulfur introduced in the form of pentanethiol (supplier Fluka®, purity>97%) and 100 ppm by weight of sulfur introduced in the form of thiophene (supplier Merck®, purity 99%). This composition corresponds to the initial composition of the reaction mixture. This mixture of model molecules is representative of a pyrolysis gasoline.

The selective hydrogenation reaction is performed in a 500-mL stainless steel autoclave, equipped with a mechanical stirrer with a magnetic drive and able to operate under a maximum pressure of 100 bar (10 MPa) and temperatures of between 5° C. and 200° C.

Prior to its introduction into the autoclave, a quantity of 3 mL of catalyst is reduced ex situ under a stream of hydrogen of 1 L/h/g of catalyst, at 400° C. for 16 hours (temperature rise slope of 1° C./minute), and then it is transferred into the autoclave, in the absence of air. After adding 214 mL of n-heptane (supplier VWR®, purity>99% HPLC Chromanorm), the autoclave is closed, purged, and then pressurized under 35 bar (3.5 MPa) of hydrogen, and brought to the temperature of the test that is equal to 30° C. At time t=0, approximately 30 g of a mixture that contains styrene, isoprene, n-heptane, pentanethiol, and thiophene is introduced into the autoclave. The reaction mixture then has the composition that is described above, and stirring is begun at 1600 rpm. The pressure is kept constant at 35 bar (3.5 MPa) in the autoclave using a reservoir bottle that is located upstream from the reactor.

The progression of the reaction is followed by the taking of samples from the reaction medium at regular time intervals: styrene is hydrogenated into ethylbenzene, without hydrogenation of the aromatic cycle, and isoprene is hydrogenated into methylbutenes. If the reaction is extended longer than necessary, the methylbutenes in turn are hydrogenated into isopentane. The hydrogen consumption is also followed over time by the reduction in pressure in a reservoir bottle located upstream from the reactor. The catalytic activity is expressed in terms of moles of H₂ consumed per minute and per gram of Ni.

The catalytic activities that are measured for the catalysts A, B and C are recorded in Table 2 below. They are related to the catalytic activity that is measured for the catalyst A (A_(HYD1)).

TABLE 2 Comparison of the Performance Values with Regard to Selective Hydrogenation of a Mixture that Contains Styrene and Isoprene (A_(HYD1)) and with Regard to Hydrogenation of Toluene (A_(HYD2)). Size of the NiO Crystallites A_(HYD1) A_(HYD2) Catalyst Compliant? (nm) (%) (%) A Yes 16.5 100 100 B No 14.1 52 63 C No 11.0 67 48

This shows well the enhanced performance values of the catalyst A that is prepared according to the invention and in particular the impact of its specific textural properties. Actually, the catalysts B and C, although having NiO crystallites that are smaller in size than those of the catalyst A, have less favorable catalytic performance values. The presence of macropores and mesopores of controlled size is therefore necessary for obtaining the enhanced performance values of the catalyst A.

Example 6 Evaluation of the Catalytic Properties of the Catalysts A, B and C with Regard to Hydrogenation of Toluene

The catalysts A, B and C that are described in the examples above are also tested in relation to the hydrogenation reaction of toluene.

The selective hydrogenation reaction is performed in the same autoclave as the one described in Example 5.

Prior to its introduction into the autoclave, a quantity of 2 mL of catalyst is reduced ex situ under a stream of hydrogen from 1 L/h/g of catalyst, at 400° C. for 16 hours (temperature rise slope of 1° C./minute), and then it is transferred into the autoclave, in the absence of air. After adding 216 mL of n-heptane (supplier VWR®, purity>99% HPLC Chromanorm), the autoclave is closed, purged, and then pressurized under 35 bar (3.5 MPa) of hydrogen and brought to the temperature of the test that is equal to 80° C. At time t=0, approximately 26 g of toluene (supplier SDS®, purity>99.8%) is introduced into the autoclave (the initial composition of the reaction mixture is then 6% by weight of toluene/94% by weight of n-heptane), and stirring is begun at 1600 rpm. The pressure is kept constant at 35 bar (3.5 MPa) in the autoclave using a reservoir bottle that is located upstream from the reactor.

The progression of the reaction is followed by taking samples from the reaction medium at regular time intervals: toluene is totally hydrogenated into methylcyclohexane. The consumption of hydrogen is also followed over time by the reduction in pressure in a reservoir bottle located upstream from the reactor. The catalytic activity is expressed in terms of moles of H₂ consumed per minute and per gram of Ni.

The catalytic activities that are measured for the catalysts A, B and C are recorded in Table 2. They are related to the catalytic activity that is measured for the catalyst A (A_(HYD2)). The enhanced performance values of the catalyst A that is prepared according to the invention are shown. 

1. Supported catalyst that comprises an oxide substrate that is for the most part calcined aluminum and an active phase that comprises nickel, with the nickel content being between 5 and 65% by weight of said element in relation to the total mass of the catalyst, with said active phase not comprising a metal from group VIB, the nickel particles having a diameter that is less than or equal to 20 nm, said catalyst having a median mesopore diameter of between 14 nm and 30 nm, a median macropore diameter of between 50 and 200 nm, a mesopore volume that is measured by mercury porosimetry that is greater than or equal to 0.40 mL/g, and a total pore volume that is measured by mercury porosimetry that is greater than or equal to 0.42 mL/g.
 2. Catalyst according to claim 1, in which the substrate has a pore volume that is contained in the pores with a diameter of between 100 and 700 nm that is less than 20% of the total pore volume of the substrate.
 3. Catalyst according to claim 2, in which the substrate has a pore volume that is contained in the pores with a diameter of between 100 and 700 nm that is less than 15% of the total pore volume of the substrate.
 4. Catalyst according to claim 1, in which the nickel content is between 10 and 34% by weight of said element in relation to the total mass of the catalyst.
 5. Catalyst according to claim 1, in which the macropore volume of the catalyst is between 5 and 40% of the total pore volume.
 6. Catalyst according to claim 1, in which the mesopore volume of the catalyst is between 0.45 mL/g and 0.8 mL/g.
 7. Catalyst according to claim 1, which does not contain micropores.
 8. Method for preparation of a catalyst according to claim 1, comprising the following steps: a) A first precipitation step, in an aqueous reaction medium, of at least one basic precursor that is selected from among sodium aluminate, potassium aluminate, ammonia, sodium hydroxide, and potassium hydroxide, and at least one acid precursor that is selected from among aluminum sulfate, aluminum chloride, aluminum nitrate, sulfuric acid, hydrochloric acid, and nitric acid, in which at least one of the basic or acid precursors comprises aluminum, the relative flow rate of the acid and basic precursors is selected in such a way as to obtain a pH of the reaction medium of between 8.5 and 10.5, and the flow rate of the acid and basic precursor(s) that contain(s) aluminum is regulated in such a way as to obtain a rate of advance of the first step of between 5 and 13%, with the rate of advance being defined as being the proportion of alumina that is formed into an equivalent of Al₂O₃ during said first precipitation step in relation to the total quantity of alumina that is formed into an equivalent of Al₂O₃ at the end of step c) of the preparation method, with said step being performed at a temperature of between 20 and 90° C. and for a period of between 2 and 30 minutes, b) A step of heating the suspension that is obtained in step a) at a temperature of between 40 and 90° C. for a period of between 7 and 45 minutes to obtain an alumina gel, c) A second step for precipitation of the suspension that is obtained at the end of step b) of heating by adding into the suspension at least one basic precursor that is selected from among sodium aluminate, potassium aluminate, ammonia, sodium hydroxide, and potassium hydroxide, and at least one acid precursor that is selected from among aluminum sulfate, aluminum chloride, aluminum nitrate, sulfuric acid, hydrochloric acid, and nitric acid, in which at least one of the basic or acid precursors comprises aluminum; the relative flow rate of the acid and basic precursors is selected in such a way as to obtain a pH of the reaction medium of between 8.5 and 10.5, and the flow rate of the acid and basic precursor(s) containing aluminum is regulated in such a manner as to obtain a rate of advance of the second step of between 87 and 95%, with the rate of advance being defined as being the proportion of alumina that is formed into an equivalent of Al₂O₃ during said second precipitation step in relation to the total quantity of alumina that is formed into an equivalent of Al₂O₃ at the end of step c) of the preparation method, with said step being performed at a temperature of between 40 and 90° C. and for a period of between 2 and 50 minutes, d) A step for filtering the suspension that is obtained at the end of step c) of second precipitation for obtaining an alumina gel, e) A step for drying said alumina gel that is obtained in step d) for obtaining a powder, f) A step for heat treatment at a temperature of between 500 and 1000° C., with or without the presence of an air stream containing up to 60% by volume of water, g) A shaping step to obtain an aluminum porous oxide substrate, h) A step for impregnating said substrate with a solution that comprises the salt(s) of the precursor(s) of the nickel-based active phase, i) A step for drying said impregnated substrate at a temperature of between 15 and less than 250° C., in such a way as to obtain a dried catalyst, j) Optionally a heat treatment of said dried catalyst at a temperature of between 250 and 1000° C. with or without the presence of water.
 9. Method according to claim 8, in which at least one step k) of reducing treatment is carried out in the presence of a reducing gas after steps i) or j) in such a way as to obtain a catalyst that comprises nickel at least partially in metallic form.
 10. Method according to claim 9, in which a step l) of passivation by a sulfur-containing compound or an oxidized compound or by the CO₂ is carried out before or after step k) of reducing treatment.
 11. Method according to claim 8, in which the rate of advance of step a) of first precipitation is between 6 and 12%.
 12. Method according to claim 8, in which the acid precursor of steps a) and c) is selected from among aluminum sulfate, aluminum chloride, and aluminum nitrate, and in which the basic precursor of steps a) and c) is selected from among sodium aluminate and potassium aluminate.
 13. Hydrogenation method in which the catalyst according to claim 1 is brought into contact in the presence of hydrogen with a hydrocarbon feedstock that contains polyunsaturated molecules and/or aromatic compounds in such a way as to obtain an at least partially hydrogenated effluent.
 14. Hydrogenation method according to claim 13, in which a selective hydrogenation is carried out at a temperature of between 0 and 500° C., at a pressure of between 0.1 and 20 MPa, at a hydrogen/(polyunsaturated compounds to be hydrogenated) molar ratio of between 0.1 and 10, and at an hourly volumetric flow rate of between 0.1 and 200 h⁻¹ for a liquid feedstock, between 100 and 15000 h⁻¹ for a gaseous feedstock of a hydrocarbon feedstock that contains polyunsaturated compounds that contain at least 2 carbon atoms per molecule and that have a final boiling point that is less than or equal to 250° C.
 15. Hydrogenation method according to claim 13, in which hydrogenation of the aromatic compounds is carried out at a temperature of between 30 and 350° C., at a pressure of between 0.1 and 20 MPa, at a hydrogen/(aromatic compounds to be hydrogenated) molar ratio of between 0.1 and 10, and at an hourly volumetric flow rate of between 0.05 and 50 h⁻¹ of a hydrocarbon feedstock that contains aromatic compounds and that has a final boiling point that is less than or equal to 650° C. 